I am a current developer working in an ES5 environment. This lecture is really a gem. Especially the prototype... wow... I wonder how it is possible to explain it so easily. It really hits the key points. It is a lecture that you can't miss. As a reference, I bought the book and watched this lecture just in case, but I wondered if I really needed to buy the book. If you are a front-end developer, buy this lecture. I highly recommend it.